1. Field of the Invention
The present invention relates to a composite magnetic material comprising a ferrite powder and a resin, and an inductor element constructed by using it. More specifically, it relates to a composite magnetic material and an inductor element advantageous for use in the electronic parts for high-frequency applications.
2. Description of the Related Art
In high-frequency circuits which are used for mobile communication devices including a portable telephone, a radio LAN, etc., inductor elements with a core coil structure for covering the frequencies up to several GHz, such as a chip inductor, are used for the purposes of impedance matching, resonance or for a choke.
However, the core coil was prepared by winding a wire around a core of a non-magnetic material, or by forming a coil pattern on a non-magnetic material, and thus it was necessary to have a large number of coil winding turns to obtain a desired impedance, resulting in a restraint toward the development of miniaturization. Since the resistance of the winding increases with increasing number of winding turns, there was also a problem that an inductor with a high Q (gain) could not be obtained.
To solve these problems, inductors having, as a core, a ferrite for high-frequency use, have been also investigated. By using a ferrite core, it is possible to decrease the number of coil winding turns in proportion to the permeability of the core material, and to realize miniaturization.
As a ferrite for high-frequency use described above, a hexagonal ferrite having an easy-to-magnetize axis in the c-plane is known. Such a hexagonal ferrite having an intrasurface magnetic anisotropy is generically termed as a ferrox planar type ferrite. A ferrox planar type ferrite is known to have a larger anisotropic constant in comparison with a spinel type ferrite, and have a permeability exceeding the frequency limit (the snoek peak).
However, even if a ferrox planer type ferrite sintered member (which is believed to have the most excellent high-frequency properties) is used as described above, there is a frequency relaxation phenomenon derived from magnetic domain wall motion, and a high Q can be maintained only when the frequency is restricted to a value up to about 300 MHz at the most.
Accordingly, the object of the present invention is to provide a magnetic material which has a larger permeability in comparison with a non-magnetic material in a frequency band of from several MHz to several GHz, and can maintain a relatively high gain Q up to a frequency band of several GHz.
Another object of the present invention is to provide an inductor element which can be miniaturized and still can provide a high Q, by using the magnetic material described above.
The composite magnetic material comprises a ferrite powder and a resin, and the ferrite powder comprises either a cobalt substituted Y type hexagonal ferrite (2BaO.2CoO.6Fe2O3) or a cobalt substituted Z type hexagonal ferrite (3BaO.2CoO.12Fe2O3), and the permeability at 2 GHz shows 90% or more of that at 1 MHz.
It is preferable that the composite magnetic material has a specific resistance of 107 xcexa9.cm or more.
The composite magnetic material is suitably used as a magnetic member of an inductor.
According to the present invention, a magnetic composite material wherein the permeability does not decrease and a high Q value can be maintained up to a GHz band can be obtained, by dispersing a cobalt substituted Y type hexagonal ferrite powder or a cobalt substituted Z type hexagonal ferrite powder in a resin.
Therefore, by using this magnetic material, it is possible to provide an inductor element which can be used up to a GHz band. Thus an inductor element which is miniaturized and still has a high Q value can be realized.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.